Subdivide face with nice random effect
This 3 modifiers produce similar effect:



We have remesh for create huge amount of square faces, next adding randomness by displace with noize texture, and decimate for creating big irregular faces. You can tune all settings to get different results.

Maybe, instead of creating geometry, try to use texture (as you suggest voronoi):



I use node group from here: Voronoi Cracks Fac?